Continuous vacuum degassing of liquids



July 22, 1969 H. L. RICHARDSON CONTINUOUS VACUUM DEGASSING OF LIQUIDS 5 Sheets-Sheet 1 Filed May 24, 1966 HARRY L. RICHARDSON INVENTOR.

7 QAQDLQ A G E N T July 22, 1969 H. RICHARDSON 3,457,064

CONTINUOUS VACUUM DEGASSING OF LIQUIDS Filed May 24, 1966 5 Sheets-Sheet 2 HARRY L. RICHARDSON INVENTOR.

AGENT July 22, 1969 H. L. RICHARDSON CONTINUOUS VACUUM DEGASSING 0F LIQUIDS 5 Sheets-Sheet 5 Filed May 24, 1966 HARRY L. RICHARDSON INVENTOR.

g; A G E N T United States Patent 3,457,064 CONTINUOUS VACUUM DEGASSING 0F LIQUIDS Harry L. Richardson, Pittsburgh, Pa., assignor to Chemical Construction Corporation, New York, N.Y., a corporation of Delaware Filed May 24, 1966, Ser. No. 552,551 Int. Cl. C22c 7/04, 7/10 U.S. CI. 75-49 8 Claims ABSTRACT OF THE DISCLOSURE Molten metals are subjected to vacuum for degassing purposes by flowing the molten metal stream through a plurality of chambers in the form of thin falling vertical or thin horizontal films, with successively higher vacuum or lower absolute pressure being provided in succeeding chambers.

The present invention relates to the continuous vacuum degassing of liquids such as molten ferrous metal, and provides an improved method for continuously removing a constituent such as a dissolved impurity from the process liquid as a desorbed gaseous component by the influence of vacuum. The method may also be applied as described herein in order to subject the liquid to a chemical or physical force or influence which may be varied in order to obtain a change in a characteristic of the liquid as a result of the vacuum atmosphere. This change may consist of physical, chemical, stoichiometric or other natural phenomena and may be caused by chemical or physical means.

One application of the invention relates to the technique and equipment to allow molten metals or metallic compounds such as ferrous products, as for instance steel, to be subjected to an artificial atmosphere in which the absolute pressure is greatly reduced below ambient atmospheric pressure. In the production of metals, and particularly in the steel industry, it has been established that a desired improvement in the quality of the finished product can be materially enhanced by so called vacuum degassing. This is used as an intermediate step to improve the quality of any and all types of steel and alloys. The objective of such a step is the removal of gases which are absorbed, or may be generated by reaction of included materials which are deleterious to the desired physical characteristics of the finished product. The established techniques, advantages, and gaseous components are well known in the industry.

The conventional practice to achieve the benefits derived from the vacuum degassing of steel involves intermittent, or so called batch processing, in which a quantity of the semi-finished material, on the order of perhaps 200 tons, is subjected to an atmosphere which approaches, as nearly as practical limits will allow, an absolute vacuum. This results in a reduction of the relative vapor pressure of the gases contained in the liquid and causes them to be discharged into the evacuated gas area by well known laws of physics. At present this result is obtained by several means, all of which require a vessel to be enclosed in a chamber which can be evacuated. This vessel may contain the raw liquid to be degassed in which case only the surface of the liquid is exposed. The bulk of the liquid is under ferrostatic pressure at varying depths below the surface of the liquid and this pressure will partially or totally overcome the effect generated by the evacuated atmosphere depending on the ferrostatic head, which is similar to a hydrostatic fluid head or pressure. With more complex equipment, a nonmagnetic or stainless steel vessel may be surrounded by a complex electrical field to generate induction stirring.

3,457,064 Patented July 22, 1969 "ice Another method in standard practice, as generally illustrated in U.S. Patent No. 2,837,790, is to place an empty ladle in a chamber which can be evacuated and to introduce a stream of the liquid into the evacuated chamber, allowing it to fall freely through a limited vertical height before entering the receiving ladle. This method is known as stream degassing. There are several other deviations from these basic procedures, all of which attempt to-secure the exposure of the maximum area of liquid surface to the evacuated area for the maximum length of time. Typical developments in this field include the procedures of U.S. Patents Nos. 2,997,760; 2,893,715; 2,882,570; 2,859,262; 2,587,793 and 2,054,923.

The present invention is an improvement based on conclusions relative to knowledge of, and existing technical faults of, existing techniques. Thus, the installed and operating costs for maintaining an evacuated area, and the removal of gases from this area to maintain the predetermined absolute pressure, increase in an exponential progression as the absolute pressure is lowered. In addition, the time required for vacuum removal of the gases from the liquid under ideal conditions is only an infinitesimal segment of the total time now required for the overall process. Gaseous equilibrium under ideal conditions is reached in less than one second in an overall treating time of some 35 minutes. Further, sequential atmospheres progressing from ambient to the final desired ultimate vacuum are desirable in order to reduce costs and time of exposure. Finally, a continuous system of degassing is highly desirable as an integrated step in the objective of making steel production a continuous process.

In the present invention, all of the conclusions mentioned supra are co-ordinated with a minimum of installed equipment and operating costs. A method is provided for the continuous vacuum removal of an impurity from a liquid stream, such as molten ferrous metal. The invention generally involves the provision of a plurality of aligned chambers, which are connected through hydrostatic liquid seals. The liquid stream flows into each chamber from the previous chamber as a thin liquid film, and thereafter flows horizontally in the chamber as a thin liquid film on a horizontally disposed surface. When the chambers are vertically aligned, the horizontally flowing liquid film is dispersed downwards into each succeeding chamber as a falling film or curtain of liquid. The liquid flows from the base of the chamber and through a lower hydrostatic liquid seal to the next succeeding chamber. The chambers are maintained at sub-atmospheric pressures with each succeeding chamber being at a lower absolute pressure than the previous chamber. Consequently, impurity is evolved in the gaseous state from the thin liquid film within each chamber and removed due to the vacuum effect, and a liquid stream of reduced impurity content is removed from the final chamber. All evacuating areas are so designed that the hydrostatic head of the liquid during treatment approaches zero to the nearest practical limit.

The principal advantage of the present invention is that the desired objective of vacuum degassing of a liquid is attained with a minimum of installed equipment and operating costs. The liquid stream is etfectively dispersed into horizontally flowng thin liquid films in each chamber, and thus equilibrium vacuum degassing is effectively and rapidly attained in each chamber. Another advantage is that the initial chambers may be maintained at a vacuum much higher than that finally desired. This will allow the bulk of the gases or gaseous impurity to be removed at a relatively low operating cost. The liquid stream is thus discharged through any number of succeeding chambers with steady progression toward the ultimate optimum vacuum atmosphere for final removal of small amounts of residual impurity. An added advantage is that the system may be designed to match plant capacity as a continuous process. Interruptions of the continuous flow rate of no consequence as the vacuum and hydrostatic liquid seals are maintained without liquid flow. In addition, when treating a liquid at elevated temperature, the system and chambers are easily preheated with a countercurrent gas flow before hydrostatic liquid seals are established. The liquid discharge may be easily plugged to allow evacuation of the entire system by the first stage evacuator or vacuum pump, with each higher vacuum evacuator or pump being activated as the hydrostatic liquid seals are established. The hydrostatic liquid seals may be evacuated for complete removal of material from the chambers by a reversal of the process ,or through external tapholes, if desired.

Each hydrostatic seal also serves as a flotation slag removal skimmer. This feature cannot be incorporated into existing processes. Finally, the relatively small size of the installation allows the use of external emergency heaters to be incorporated into the system at a very nominal cost.

It is an object of the present invention to provide an improved method for the continuous vacuum degassing of liquids.

Another object is to remove impurity from a liquid stream in an improved manner by vacuum degassing.

A further object is to degass a liquid by disposing the liquid as a thin film which is subjected to vacuum.

An additional object is to attain vacuum degassing of a liquid in a plurality of stages within chambers main tained at successively lower pressure levels and in which the liquid is disposed as a thin film.

Still another object is to degass a liquid in a plurality of connected chambers in which the liquid is exposed to vacuum as a horizontal film and a vertical falling film.

An object is to provide an improved method for the continuous vacuum degassing of molten ferrous metal in a plurality of connected chambers maintained at successively lower pressure levels.

These and other objects and advantages of the pres ent invention will become evident from the description which follows. The invention will be described relative to a preferred application, consisting of the continuous vacuum degassing of molten ferrous metal such as steel.

Referring to the figures:

FIGURE 1 is a sectional elevation view of one embodiment of the invention, and

FIGURE 2 provides an isometric elevation view of an alternative embodiment of the invention, and

FIGURES 3 and 4 provide sectional elevation views of still another embodiment of the invention.

Referring now to FIGURE 1, molten steel or other ferrous metal stream 1 is continuously passed through an opening in retention wall 2 and joins a pool of molten steel which is retained by lip 3 on the upper surface of the container cover 4. The molten steel flows under liquid seal baffle 5, which serves to provide a hydrostatic liquid seal for the first vacuum chamber under cover 4. The molten steel next flows over the upper edge of lip 3 and then flows downwards as a thin liquid film into the first vacuum chamber defined by cover 4, container wall 6 and horizontal partition 7. A vacuum is maintained within the first chamber by induction through nozzle 8, with the gases evolved from the molten steel within the chamber, such as hydrogen, nitrogen and oxygen, being withdrawn via stream 9 and passed through unit 10, which consists of a vacuum pump, steam ejector, or other suitable vacuum-inducing device. Stream 9 will usually consist of a major proportion of the impurities in stream 1.

The thin liquid film of molten steel flowing downwards from lip 3 flows onto the horizontally disposed baffle 11, and then flows across the upper surface of baffle 11 as a thin liquid film or layer of molten metal, and is thus further exposed to the vacuum effect generated by unit 10. The shallow pool or layer of molten steel on the upper surface of baffle 11 is preferably retained by outer liquid retention lip 12. The molten steel next flows over the upper end of lip 12 and downwards as a thin liquid film adjacent to lip 12 and liquid seal bafile 13, which extends downward from the horizontal bafile 11 into the pool of molten steel retained on the upper surface of partition 7 by retention lip 14. The lip 14 extends upwards from the central opening in partition 7 and terminates above the lower end of bafile 13, so as to maintain a liquid level above partition 7 of suflicient height to insure a hydrostatic or ferrostatic liquid seal, which is maintained by liquid seal bafile 13.

The molten steel flows under the lower end of baffle 13 and over the upper end of lip 14, thereafter flowing downwards as a thin liquid film into the second vacuum chamber below partition 7. A vacuum effect is maintained within the second chamber by induction through nozzle 15, and the vacuum level in the second chamber is maintained greater than in the first chamber defined by sections 4, 6 and 7, in other words, the absolute pressure in the second chamber is lower than in the first chamber. The gases evolved from the molten steel within the second chamber below partition 7 are withdrawn via stream 16 and passed through vacuum-inducing unit 17, which may be similar to unit 10 described supra. Although stream 16 is removed at a greater vacuum level than stream 9, the total work requirement for the removal of stream 16 is substantially lessened, due to the prior removal of the bulk of impurities via stream 9.

The thin liquid film of molten steel flowing downwards from lip 14 flows onto the horizontally disposed baflle 18, and then flows across the upper surface of baffle 18 as a thin liquid film or layer of molten metal, and is thus further exposed to the vacuum effect generated by unit 17. The shallow pool or layer of molten steel on the upper surface of baflle 18 is preferably retained by outer liquid retention lip 19. The molten steel next over the upper end of lip 19 and downwards as a freely falling film of molten steel, which is consequently extensively exposed to vacuum degassing. The molten steel then flows into the pool of molten steel retained on the upper surface of partition 20 by retention lip 21. The lip 21 extends upwards from the central opening in partition 20 and terminates above the lower end of liquid seal baffle 22, which extends downward from the horizontal baflle 18 into the pool of molten steel which is retained on partition 20 and thus provides a hydrostatic liquid seal.

The molten steel flows under the lower end of bafile 22 and over the upper end of lip 21, thereafter flowing downwards as a thin liquid film into the third vacuum chamber below partition 20. A vacuum effect is maintained within the third chamber by induction through nozzle 23, and the vacuum level in the third chamber is maintained greater than in the second chamber below partition 7, in other words, the absolute pressure in the third chamber is lower than in the second chamber. Since the third chamber below partition 20 is the lowest and final vacuum chamber, in which final and thorough vacuum degassing is attained, in most instances the absolute pressure in the third chamber is maintained below 0.015 kg./sq.cm. The residual and final gases evolved from the molten steel within the third chamber below partition 20 are withdrawn via stream 24 and passed through vacuum-inducing unit 25, which may be similar to unit 10 described supra. Although stream 24 is removed at a greater vacuum level or lower absolute pressure than streams 9 and 16, the total work requirement for the removal of stream 24 is substantially lessened, due to the prior removal of the bulk of impurities via streams 9 and 16.

The thin liquid film of molten steel flowing downwards from lip 21 flows onto the horizontally disposed baffle 26, and then fiows across the upper surface of baffle 26 as a thin liquid film or layer of molten metal, and is thus further exposed to the vacuum effect generated by unit 25. The shallow pool or layer of molten steel on the upper surface of baffle 26 is preferably retained by outer liquid retention lip 27. The molten steel next flows over the upper end of lip 27 and downwards as a freely falling film of molten steel, which is consequently extensively exposed to vacuum degassing. The molten steel then falls into the pool of molten steel retained on the upper surface or partition 28 by retention lip 29. The lip 29 extends upwards from the central opening in partition 28 and terminates above the lower end of liquid seal baffle 30, which extends downward from the horizontal baffle 26 into the pool of molten steel which is retained on partition 28 and thus provides a hydrostatic liquid seal.

The molten steel flows under the lower end of baifie 30 and over the upper end of lip 29, thereafter flowing downwards into the pool of completely degassed molten steel retained in the bottom section 311 of the treating unit. Product degassed molten steel is continuously withdrawn from lower nozzle 32 via stream 33, and passed to product utilization. Any slag which may accumulate in section 31 above the pool of molten steel is periodically removed from side nozzle 34 as stream 35.

Referring now to FIGURE 2, a simplified version of the vacuumdegassing assemblage is presented in isometric elevation view. The feed stream 36 consisting of molten liquid steel is passed via opening 37 into the vacuum degassing container defined by roof 38, walls 39, 40 and 41 and floor 42. The molten steel is diverted by horizontal bafile 43 into liquid pools retained by partitions 44 and 45 and retention lips 46 and 47, with a hydrostatic liquid seal being formed by the extension of liquid seal baffies 48 and 49 downwards to a terminus below the upper ends of lips 46 and 47. An additive stream 50 consisting of manganese, chromium or other desired alloying or purifying agent is passed via inlet nozzle 51 into the pool of liquid maintained above partition 45. However, some of these additives are for purification and some for final alloying. The more volatile materials may be added further through the system as this process allows rapid mixing of these materials in minimum time.

The molten steel flows under bafiies 48 and 49 and over the upper end of retention lips 46 and 47, and then flows downwards as a thin liquid film into the first vacuum degassing chamber below partitions 44 and 45. The molten steel is diverted by horizontal baffle 52 and flows as a thin liquid film into liquid pools retained by partitions 53 and 54 and retention lips 55 and 56, with a hydrostatic liquid 1 purity through nozzle 59 as stream 60, in a manner similar to that described supra.

The molten steel flows'under baffles 57 and 58 and over the upper end of retention lips and 56, and then flows downwards as a thin liquid film into the second vacuum degassing chamber below partitions 53 and 54. The molten steel is diverted by horizontal baffle 61 and flows as a thin liquid film into liquid pools retained by partitions 62 and 63 and retention lips 64 and 65, with a hydrostatic liquid seal being formed by the extension of liquid seal bafiles 66 and 67 downwards to a terminus below the upper ends oflips 64 and 65. A vacuum effect which consists of a lower absolute pressure than that of the first vacuum chamber is maintained in the second chamber by induction of desorbed gases or other impurity through nozzle 68 as stream 69, in a manner similar to that de- Referring now to FIGURE 3, an alternative arrangement involving substantially horizontal flow of the liquid steel as a thin liquid film is illustrated. The molten steel is passed via tundish 76 into an opening in the roof 77 of vessel 78, which consists of a suitable molten steel retention vessel such as a ladle. The molten steel flows downwards from tundish 76 into vessel 78 and joins a pool of molten steel in unit 78, which serves to provide a hydrostatic head for liquid flow through the system. A vacuum is maintained within unit 78 by the provision of suitable vacuum means as described supra, which serves to remove volatile impurities stream 79 via nozzle 80. Vessel 78 is the first of four vacuum chambers. The gross removal of impurities occurs in this hogging chamber. Gas evolution is usually of such a magnitude that an explosive ellervescence requires a relatively large area or volume and may require the provision of spray shields, not shown, adjacent to the inlet of nozzle 80. The liquid flows past lower tap-hole 81 disposed in the bottom of unit 78, and next flows through an opening in the lower part of the wall of unit 78. The molten steel thus flows into the first chamber of the preferably cylindrical and horizontally aligned container 82. The first chamber is defined by container 82, the wall of vessel 7 8, and the substantially vertical partition 83. The liquid flows upwards into the first chamber past step 84, and then fiows substantially horizontally across bottom section 85 as a thin liquid film. A vacuum is maintained within the first chamber by the provision of suitable vacuum means as described supra, which serves to remove volatile impurities stream 86 via nozzle 87. The vacuum level is greater in the first chamber than in the vessel 78, that is, a lower absolute pressure is maintained in the first chamber than in vessel 78.

The liquid molten steel next flows under the lower end of partition 83 and upwards past the step 88, and into the second chamber defined between partition 83 and the substantially vertical partition 89. The liquid then flows substantially horizontally across bottom section 90 as a thin liquid film. A vacuum is maintained within the second chamber by the provision of suitable vacuum means as described supra, which serves to remove volatile impurities stream 91 via nozzle 92. The vacuum level is greater in the second chamber than in the first chamber, that is, a lower absolute pressure is maintained in the second chamber than in the first'chamber.

The liquid molten steel next flows under the lower end of partition 89 and upwards past the step 93, and into the third chamber defined between partition 89 and the outlet end 94 of the container 82. The liquid then flows substantially horizontally across bottom section 95 as a thin liquid film. A vacuum is maintained within the third chamber by the provision of suitable vacuum means as described supra, which serves to remove volatile impurities stream 96 via nozzle 97. The vacuum level is greater in the third chamber than in the second chamber, that is, a lower absolute pressure is maintained in the third chamber than in the second chamber. The third chamber will preferably be maintained at an absolute pressure of less than 0.015 kg./sq. cm.

The fully degassed and substantially impurity-free liquid now flows from the third chamber past level controller 98, and is collected in atmospheric seal leg 99 for subsequent product utilization. The atmospheric seal leg 99 may consist of a balanced U-seal, or the rising leg of the seal 99 may be truncated to allow the level controller 98 to control the discharge flow of the substantially impurity-free liquid by suitable means such as a stopper rod, not shown.

The area adjacent and external to seal leg 99 may be flooded with inert gas to prevent recontamination during conventional casting or during flow into a continuous casting device.

On shut-down of the system, which may be necessitated by a change of heats or alloy composition, the facility is readily drained free of residual molten metal and slag, by

7 the opening of tap hole 81. In this case, the liquid flow will be reversed, and the residual liquid steel and slag will flow down the steps 93, 88 and 84. The slag originally present in the molten steel fed to the tundish 76 is effectively skimmed off by the partitions 83 and 89, which also cooperate with the steps 88 and 93 respectively to provide hydrostatic liquid seals between the chambers. Residual metal in leg 99 may be removed through an auxiliary taphole, not shown.

FIGURE 4 is a sectional elevation view of the container 82, taken on section 44 of FIGURE 3, and shows the preferable cylindrical nature of the container 82, as well as the partition 89. FIGURE 4 also demonstrates the minute amount of liquid retained in the vessels to maintain interchamber seals.

Numerous alternatives within the scope of the present invention will occur to those skilled in the art. Thus, although the method is particularly applicable to the vacuum degassing of molten steel, other applications in the degassing or selective removal of a specific component or impurity from a liquid stream, either at elevated, ambient or sub-ambient refrigerated temperatures, will be evident to those skilled in the art. The lips 12, 19 and 27 may be omitted in suitable instances, such as in the configuration of FIGURE 2. Additives may be added to the liquid stream in each of the chambers if desired. While a maximum vacuum or lowest absolute pressure of less than 0.015 kg./sq. cm. is preferred in the last and lowest vacuum chamber, a higher pressure for final vacuum degassing may be provided in this chamber in suitable instances. The number of vacuum chambers to be provided in practice, with successively reduced absolute pressure levels in succeeding chambers, will depend on the circumstances of a particular installation. Thus, three vacuum chambers are provided in the assemblage of FIGURE 1, while only two vacuum chambers are provided in FIG- URE 2. In some instances, more than three chambers may be provided, however due to the exposure of the liquid to continuous vacuum degassing as a thin vertical and horizontal film in the present invention, rapid impurity removal and equilibrium is attained in each chamber, and consequently three chambers will usually sufiice in most instances.

An example of an industrial application of the present invention to the continuous vacuum degassing of steel will now be described.

Example The apparatus of FIGURE 3 was designed for a proce-ss stream consisting of 9,000 kg./minute of molten steel at a temperature of 1620 C., which was subjected to vacuum degassing as illustrated in FIGURE 3. The initial process stream contained dissolved impurities consisting of approximately 6.8 p.p.m. hydrogen, 60 p.p.m. nitrogen and 275 p.p.m. oxygen. The four vacuum chambers were designed for absolute pressures of approximately 0.112, 0.042, 0.014 and 0.0014 kg./sq. cm. respectively. The four vacuum chambers removed about 60, 20, 8 and 4% of the total dissolved impurities respectively. The final fully degassed molten steel product contained only very minor residual proportions of impurities, and was a high quality finished steel suitable for continuous casting.

I claim:

1. A method for the continuous vacuum removal of an impurity from a molten metal stream which comprises flowing said molten metal stream downwards through a plurality of vertically aligned and connected chambers, each of said chambers being separated from the next lower chamber by a hydrostatic molten metal seal, said molten metal stream flowing downwards into each chamher as a thin molten metal film, and thereafter flowing horizontally as a thin molten metal film on a horizontally disposed baflle within each chamber, said bafile terminating in proximity to the wall of said chamber whereby the horizontally flowing thin molten metal film is dispersed downwards into each chamber from the respective horizontal baflle as a falling film of molten metal and flows from the base of each chamber through a lower hydrostatic molten metal seal to the next succeeding chamber, said chambers being maintained at sub-atmospheric pressures with each succeeding chamber being at a lower absolute pressure than the previous chamber, whereby said impurity is evolved from the thin molten metal film within each chamber in the gaseous state, and removing a molten metal stream of reduced impurity content from the lowest chamber.

2. The method of claim 1, in which said molten metal stream comprises molten ferrous metal.

3. The method of claim 2, in which said impurity is selected from the group consisting of hydrogen, nitrogen and oxygen.

4. The method of claim 1, in which the absolute pressure in the lowest of said chambers is below 0.015 kg./

sq. cm.

5. The method of claim 1, in which an additive component is introduced into said molten metal stream in at least one of said chambers.

6. A method for the continuous vacuum removal of an impurity from a molten metal stream which comprises flowing said molten metal stream through a plurality of connected chambers, said chambers being juxtaposed in a substantially horizontal plane with each of said chambers being separated from the next succeeding chamber by a molten metal seal, the first of said chambers being provided with a lower taphole, said taphole being closed during the flow of said molten metal stream through said chambers, said molten metal stream flowing horizontally as a thin molten metal film on the floor of each chamber, and thereafter flowing through a molten metal seal to the next succeeding chamber, with the floor of each succeeding chamber being elevated above the floor of the previous chamber, maintaining a sub-atmospheric pressure level within each chamber, with each succeeding chamber being at a lower absolute pressure than the previous chamber, whereby said impurity is evolved from the thin molten metal film within each chamber in the gaseous state, removing a molten metal stream of reduced impurity content from the final chamber, said final chamber being maintained at lowest absolute pressure, and thereafter terminating the flow of said molten metal stream, and opening said taphole, whereby a'reversal of molten metal flow takes place within said chambers to produce reverse drainage flow of residual molten metal from all of said chambers through said taphole.

7. The method of claim 6, in which said molten metal stream comprises molten ferrous metal.

8. The method of claim 6, in which the absolute pressure in the final chamber is below 0.015 kg./sq. cm.

References Cited UNITED STATES PATENTS 2,859,262 11/1958 Harders et al. -49 X 2,882,570 4/1959 Brennan 75-49 X 3,342,250 9/ 1967 Treppschuh et al. 75-49 X 3,343,828 9/1967 Hunt 26634 3,367,396 2/ 1968 Sickbert et al. 75-49 X FOREIGN PATENTS 683,996 3/1930 France. 964,734 7/1964 Great Britain.

L. DEWAYNE RUTLEDGE, Primary Examiner HENRY W. TARRING II, Assistant Examiner U.S. Cl. X.R. 75-93; 266-34 

